There was an exodus of voters, just not ones who identify as leftwing. That’s the thing, though: Even Americans who don’t consider themselves leftist want leftwing stuff (universal healthcare, no genocide in Gaza, etc). Self-identified leftists/progressives are more likely to hold their noses and vote for the establishment, but “centrists” who want many of the same things are willing to stay home, so that’s where the electoral losses happen. In this specific case, post-election polling does show that Harris would’ve won if she had promised a ceasefire.